Clean and cut vegetables in two parts; then remove the upper layer by leaving a 1 cm edge, and remove all seeds. Put vegetables on a tray covered with baking paper, add oil, salt and pepper, then put in the oven at 180° C for 25 minutes. When cooked, remove from the oven.
Open glass jars and drain tuna by placing it within a vessel.
In a bowl, pour cereals and garnish with minced parsley, capers, oil, salt and pepper. Mix and incorporate a part of tuna. Amalgamate and fill the vegetables.
Finish with the remaining parts of tuna, some parsley leaves and one caper. Drizzle with a little oil, then serve.